1. Field of the Invention
The present invention relates to powder mixtures based on calcium phosphates. The invention also relates to the use of the aforesaid powder mixtures for manufacturing biocements with high solubility which only contain the crystal phases currently known after setting, i.e. hydroxyapatite (HA), precipitated apatite (PHA) and calcium-deficient hydroxyapatite (Ca-d-HA), in subordinate amounts, i.e. as secondary phases.
2. Description of the Related Art
In principle, inorganic materials which are easily resorbed are known. Materials which are specifically used as bioactive bone replacement materials and dissolve quickly have also been described in the relevant literature. For example, there have been numerous publications dedicated to the successful clinical use of ceramic materials the main crystal phases of which are alpha- or beta-tricalcium phosphate (TCP). In addition, there have been comparative analyses of these two TCP phases using animal tests. With regard to the following explanations, special attention must be drawn to an alpha-TCP containing dicalcium phosphate on the surface of granulated materials made thereof, whose solubility was higher than that of the pure alpha-PCT core material, especially in the initial phase following an implantation (EP 0237043 B1).
The chemical solubility of the aforesaid granulated materials was surpassed by other bioactive materials based on calcium phosphates which in addition contain oxides of potassium, sodium, magnesium and/or silicon (EP 541564 B1) and the glassy-crystalline material of which is based on the following main crystal phases: Phase X, rhenanite, phase according to Ando (Phase A) and/or mixed crystals derived from the aforesaid phases.
The aforesaid products are obtained by melting processes, they contain orthophosphates and a glass phase and their individual phase constituents are distributed in a homogenous manner, but they are not known to have been processed into cements.
Instead, inorganic biocements have been composed using powder mixtures made up of various calcium phosphates, as disclosed e.g. in EP 1153621 or U.S. Pat. No. 5,129,905.